I would go with a double batting, cotton and maybe wool. All natural. Poly... it has a melting/ burning issue. I would go with natural fibers.
I used Hobbs 80/20 and their washable wool.
Also, I have heard when you quilt a baby's quilt not to use poly thread. If the thread has a tail, a baby will sometimes start wrapping their finger around it, and can damage the finger, even to the point of losing it.
Would never have thought of this, but I have read of it in a Quilt magazine.